The need for an arterial barrier or filter to prevent embolization of particles down-stream from the area being treated in the arterial system is well known, e.g., in percutaneous transluminal angioplasty (PTA). This need became especially clear and more urgent as the procedure of PTA (catheter based) treatment of the carotid arteries became more common. One of the major risks of stenting in the carotid arteries is the danger of emboli drifting downstream from the area being treated and causing transient ischemic attack(TIA). Several conventional devices have been utilized to try and prevent this danger to the patient. These devices are passive devices. One such conventional device is a balloon mounted on a catheter or on a guide wire that is inflated distal to the lesion being treated. Another such conventional device is an umbrella like filter placed distal to the lesion being treated. A major shortcoming of these conventional filters is that these conventional filters or barriers may greatly reduce, or even block, the downstream flow of blood from the treated artery to the brain, e.g., in the carotid artery. Another shortcoming of these devices is that they are passive.